1. Field of the Invention
The present invention relates to a liquid crystal display module, and more particularly, to a liquid crystal display module capable of improving luminance of a liquid crystal panel by enhancing a light transmittance.
2. Discussion of the Related Art
An application field of liquid crystal display device (hereinafter, referred to as ‘LCD device’) has been gradually expanded owing to various advantages such as lightness in weight, thin profile, and low-driving power. In recent years, the LCD device is widely used for office automation devices, multimedia devices, and information communication devices.
A liquid crystal display module of the LCD device includes a liquid crystal panel which is provided with liquid crystal cells arranged in a matrix-type configuration between two glass substrates; and a backlight unit for supplying light to the liquid crystal panel.
The liquid crystal panel displays images by controlling a light transmittance according to a video signal applied to control switches such as thin film transistors (TFT) arranged in a matrix-type configuration. At this time, the liquid crystal panel cannot emit light in itself. Thus, the liquid crystal panel is supplied with the light emitted from the backlight unit including a light source, wherein the light source included in the backlight unit may be positioned at a rear side or lateral side of the liquid crystal panel.
The backlight unit can be classified into a direct type and an edge type according to the position of the light source. In more detail, the direct type backlight unit includes the light source positioned at the rear side of the liquid crystal panel; and the edge type backlight unit includes the light source positioned at the lateral side of the liquid crystal panel.
FIGS. 1 and 2 illustrate a related art liquid crystal display module. FIG. 3 is a cross section view along A-A′ of FIG. 2. FIGS. 1 and 2 show an edge-type backlight unit using a light-emitting diode (LED) as a light source.
Referring to FIGS. 1 to 3, the related art liquid crystal display module includes a liquid crystal panel 40 for displaying images by controlling a light transmittance of liquid crystal according to input video data; a light source 10 for supplying light to the liquid crystal panel 40; a lower polarizing plate 20 for polarizing the light emitted from the light source 10; a light-guiding plate 30 for guiding the light incident on its lateral side to a frontal direction of the liquid crystal panel 40; and an upper polarizing plate 50, positioned above the liquid crystal panel 40, for polarizing the light outgoing from the liquid crystal panel 40.
The liquid crystal panel 40 includes a lower glass substrate 41 on which control switches such as thin film transistors (TFT) are formed; an upper glass substrate 45 on which a color filter layer 44 is formed; a spacer (not shown) for maintaining a constant cell gap between the lower and upper glass substrates 41 and 45; a liquid crystal 42 filled in a space prepared by the spacer; and an over-coating layer 43 formed between the liquid crystal 42 and the color filter layer 44.
The liquid crystal panel 40 cannot emit the light in itself. Thus, the liquid crystal panel 40 displays the images by controlling the transmittance of light emitted from the light source 10. One of the most important points to be duly considered for improvement of the picture quality of the images displayed in the liquid crystal panel 40 is luminance of the light irradiated on the liquid crystal panel 40. That is, the light with high luminance has to be supplied to the liquid crystal panel 40, to thereby obtain the high picture quality in the displayed images.
In the related art liquid crystal display module having the aforementioned structure, the light emitted from the light source 10 comes out from the liquid crystal display module after traveling through the lower polarizing plate 20, the light-guiding plate 30, the liquid crystal panel 40, and the upper polarizing plate 50, whereby the luminance of light finally outgoing from the liquid crystal panel 40 is lowered considerably.
If the liquid crystal panel 40 has 13.3-inch (113 pixels per inch) size, the light transmittance of each of the lower and upper polarizing plates 20 and 50 is 45%; the light transmittance of each of the lower and upper glass substrates 41 and 45 is 94%; the light transmittance of TFT array and pixel on the lower glass substrate 41 of the liquid crystal panel 40 is 65%; and the light transmittance of color filter layer 44 of the liquid crystal panel 40 is 27%.
Eventually, the light outgoing from the liquid crystal panel 40 is only about 7˜8% of the light emitted from the light source 10, whereby the light transmittance becomes low. Meanwhile, if the liquid crystal panel 40 has 32-inch (49 pixels per inch) size, the light outgoing from the liquid crystal panel 40 is about 5% of the light emitted from the light source 10, whereby the light transmittance becomes considerably lowered.
The related art liquid crystal display module is disadvantageous in that most of light emitted from the light source 10 is lost by passing through the lower polarizing plate 20, the upper polarizing plate 50, and the color filter layer 44, included in the liquid crystal panel 40, having the aforementioned light transmittances. Thus, the light efficiency of the related art liquid crystal display module is lowered by the light loss.
In order to overcome this problem, the plural light sources 10 may be additionally arranged in the backlight unit, to thereby improve the luminance of the liquid crystal display module. However, a manufacturing cost of the liquid crystal display module is increased due to the additionally-provided light sources 10. Also, if additionally driving the plural light sources 10, power consumption is highly increased.